Abstract: PURPOSE:To make the impact value of the title ductile iron higher than that of the conventional alloy tool steel by adding Mo, V, W, etc., separately or compositely to the base alloy component of the ductile iron, and then austempering the iron under specified conditions. CONSTITUTION:The base alloy component contains, by weight, 3.0-4.0% C, 2.0-3.5% Si, 0.1-0.9% Mn, =0.5hr, and austempered. The ductile iron has high wear resistance, and can be used for the punching die, etc., for cold pressing and various sliding parts.

Abstract: PURPOSE:To obtain a ferrous casting excellent in castability and having high strength, high hardness, and high toughness by applying austempering treatment to a ferrous casting material having high Si content and containing specific amounts of B so as to form this material into a structure of bainite and residual austenite in which spheroidal graphite is dispersed. CONSTITUTION:A casting member having a composition consisting of, by weight, 0.5-2.5% C, 1.0-4.0% Si, <0.6% Mn, <0.05% S, 0.01-0.1% B, and the balance Fe is subjected to austempering treatment. Since a matrix structure in which flake graphite is spheroidized by the presence of B and uniformly dispersed and which is composed of bainite and residual austenite is formed, the ferrous casting member having high Si content, excellent in castability, and improved in strength, hardness, and toughness can be obtained.

Abstract: The use of gears for power transmission is conditioned by the strength as well as the accuracy. The employment of austempered ductile iron is examined from this view point. The test gears are made of ductile irons FCD45 and FCD60. They are austenized at 900°C then austempered at 300 to 400°C. In the austempering process, the bainitic transformation causes size expansion and a considerable tooth profile error of the gears. The profile error can be reduced by austempering at 400°C or employing the ferrite-bainite dual phase ductile iron. The bending fatigue tests are performed by using electro hydraulic servo controlled pulsators, and SN curves are obtained. The higher the austempering temperature, the higher the fatigue strength. The fatigue strength of gears austempered at 400°C is about 520MPa and it is higher than the strength of normalized S45C gears.

Abstract: PURPOSE:To improve workability and also to prevent deterioration in physical properties, such as toughness and fatigue strength, by austenitizing a spheroidal graphite cast-iron stock, quenching this stock to carry out isothermal transformation treatment, cooling the above, and then heating the above to the prescribed temp. to apply tempering. CONSTITUTION:After austenitizing treatment is applied to a spheroidal graphite cast-iron stock, is subjected to austempering treatment consisting of isothermal transformation treatment in which quenching is performed by immersion in a cooling medium and also of air cooling. By the above treatment, the metallic structure of the stock is transformed to a mixed structure of bainite and residual austenite. Then, heating is applied to the above at 250-400 deg.C to carry out tempering, by which martensite contained in residual austenite is transformed to another structure. This stock is machined so as to be formed into a spheroidal graphite cast-iron product.

Abstract: By classical definition, bainite is a mixture of carbide and ferrite. But ADX shows an intermediate structure formed during the austenite decomposition to bainite. The presence of retained austenite (RA) affects the mechanical properties of the casting. The stability of the unreacted austenite depends on the content of carbon, silicon and gamma-phase-extending alloying elements, such as nickel. The amount of RA is proved to be about 40 vol.-% depending on the austempering time.

Abstract: Austempered ductile irons (ADI) are a high strength, high toughness ductile cast irons with vastly improved mechanical properties. Various grades of austempered ductile irons can be produced depending primarily on the heat treatment conditions. The mechanical properties of austempered ductile irons are described and compared to the properties of other competing materials. The fundamentals of the physical metallurgy of the austempering reaction in ductile irons will also be reviewed to highlight important aspects of ADI process control and quality assurance. Heat treatment control during austempering is much more critical than for other ferrous heat treating operations. In recent years austempered ductile irons have successfully been used to replace steel components and to upgrade conventional ductile iron components for a wide variety of applications. Specific applications are highlighted which illustrate the particular advantages of austempered ductile irons.

Abstract: The mechanical properties and structure of bainite and martensite af-ter tempered in 6-5-4-2 high speed steel have been investigated. It was found thatthe secondary hardening effect and resistance to heat softening as well as impacttoughness are higher in the bainite than in the martensite. TEM observations showthat the Fe_3C precipitated in the martensite after temrering at the temperaturenear the peak of hardening-tempering temperature curve. However, no Fe_3C but thedispersive MC and M_2C precipitated in the ferrite and austenite of bainite aftertempering at the same temperature. This shows the diffusion of alloy elements form-ing carbide must be taken during the process of bainite growing.

Abstract: The variations of microstructures and mechanical properties of steels 15CrMnMoV, 18Mn2CrMoB,18Cr2Ni4W,30CrMnSi,30CrMnSiNi2 and 40CrMnSiMoV,which were tempered at different temperatures after austempering and continuous cooling at given rates, have been investigated.Based on the experimental results,the behaviour and mechanism of tempered bainite embrittlement(TBE)have been discussed.Finally,the theoretical and prac- tical basis for selecting the optimum tempering temperature of steels with bainite structure af- ter heat treatment are proposed.

Abstract: PURPOSE:To drastically facilitate the balance working by locally forming non- austempering treated parts on the balance weight part of a crankshaft to be subjected to an austempering treatment and rendering the material easy to work. CONSTITUTION:A heat insulating jig 4, e.g., is fixed on the balance weight part 3 of the crankshaft M worked into the prescribed shape. The cooling ratio in the fixed part of the jig 4 is slowed at the time of subjecting said shaft M to the austempering treatment. High strength and high toughness are then provided on the surface of the shaft M except the fixed part of the jig 4. The non-austempering treated parts are locally formed on the part fixed with said jig 4 as well to facilitate the working.

Abstract: PURPOSE:To form a structure into bainite and to manufacture a high-hardness piston material, by subjecting a continuously cast pipe of ductile cast iron to hardening treatment directly after casting and successively to austempering treatment at the time of manufacturing piston material for rotary compressor. CONSTITUTION:Molten ductile cast iron is cast continuously into a long-size pipe, and the resulting ductile cast iron pipe of >=900 deg.C directly after casting is subjected to hardening treatment by means of rapid cooling such as water cooling. Successively, this pipe is immersed into a hot bath of 300 deg.C, at and above the Ms point, and austempered to form the structure into bainite, and then cooled down to room temp. By this method, the piston material for rotary compressor having 40-58 Rockwell hardness HRC can be obtained.

Abstract: This paper discusses the hobbing of gears made of austempered ductile iron (spheroidal graphite iron), which has recently, become the object of attention as a new material for gears. This iron has many advantages, such as a high strength equivalent to steels, and is an economical material. The cutting of teeth of a hardened gear blank is considered to be very difficult, yet if it be possible, the production cost will be lower because the gear can be used without a finishing operation on the tooth surface, removing the distortion caused by the heat treatments. In cutting tests, at first a basic test was conducted using a fly-tool of the same form as that of one blade of a hob. As a result, it was found that hobbing can be performed by using a tool with a large clearance angle (20°).

Abstract: OF THE DISCLOSURE An austempered ductile iron composition with a mixed austenitic-bainitic structure is made by a method which enables the iron to withstand high cyclical stresses while having a high resistance to abrasion. Articles such as automobile roller-follower camshafts that are made from the iron alloy may have portions thereof selectively austempered to reduce the overall cost and time required to manufacture the article.

Abstract: The effects of volume and mechanical stability of retained austenite in 60Si2Mn steel austempered on the resistance to hydrogen-induced cracking (HIC) is studied in the paper. The hydrogen embrittlement properties are shown by the threshold stress intensity factor Kth of sustained load hydrogen embrittlement and brittleness ratio IH of dynamic load hydrogen embrittlement. The results show that Kth is not affected by volume of retained austenite (8.4 to 17.9%) in the steel austempered remarkably, the mechanical stability of retained austenite is decreased and the resistance of the steel to hydrogen embrittlement is affected by tempering and charging after austempering. The hydrogen–induced cracking happens easily and the voids form in the martensite transformed from the blocky retained austenite under the action of stress. The stress at the tip of carck is relaxed and the resistance to HIC is improved since the voids form in the martensite. On the other hand, the fracture happens easily since the voids in martensite serve as the path of crack propergation. The difference between Kth and IH is also discussed in the paper. There have been some reports on the effects of austempering and retained austenite on the resistance hydrogen embrittlement. There exists plenty of retained austemite in the microstructure of 60Si2Mn steel austempered since the traneformation from austenite to bainite can not be finished completely during austempering. Ritchie (1978) considered that retained austenite had no remarkable effect on thresold stress intensity factor K1scc but decreased crack growth rate in region II II by one to two orders of magnitude. During deformation, retained austenite transformed to martensite which affected greatly the hydrogen embrittlement cracking. The paper aims to study the factors which affect the mechanical stability of retained austenite and the effect of the mechanical stability of retained austenite on the resistance to hydrogen embrittlement.

Abstract: Recently developed austempered ductile irons have good mechanical properties. Comparing the austempered ductile irons with the normal ductile irons the austempered ductile irons have about two times or higher tensile strength than the normal ductile irons at the same level of elongation as shown in Fig.l [1]. Austempered ductile irons are made from ductile cast irons by austempering heat-treatment. Ideally, during austempering, the ductile cast irons are cooled rapidly from the austenitizing temperature to the temperature range for bainite formation, avoiding the zone of pear-lite formation. However, wide spread use of austempered ductile irons have not yet occurred. The main problem is in the difficulties of identifying and controlling the austempering heat-treat — ment parameters to achieve optimum properties consistently [1]. Those heat-treatment parameters are austenitizing temperature, austempering temperature, and austempering holding time. Austempering reaction of ductile cast irons is usually divided into two stages. First stage is toughening stage. Austenite decomposes into bainitic ferrite and carbon riched austenite. These two phase mixture of bainitic ferrite and austentie is the reason for the outstanding mechanical properties of austempered ductile irons.

Abstract: Recent research on austempered ductile irons (ADI) has been reviewed. The physical metallurgy of the austempering reaction and the important effects of alloying elements are discussed, along with a...